1. Field of the Invention
The present invention generally relates to a flat panel display device having electrodes and a luminous layer. This invention may be embodied, for example, in a television set or a calculator, but it will be appreciated that it is also useful in other applications.
2. Description of the Prior Art
Many of the patents issued in various countries recognize the need for employing a support inside the evacuated flat panel display device in order to make the display device withstand the atmospheric pressure.
For example, U.S. Pat. No. 4145633 which was issued to Peters et al. on Mar. 20, 1979 is typical of such systems, as are U.S. Pat No. 4341980 which was issued to Noguchi et al. on July 22, 1982; U.S. Pat. No. 4356427 which was issued to Noguchi et al. on Oct. 26, 1982; U.S. Pat. No. 4622492 which was issued to Barton on Nov. 11, 1986; and U.S. Pat. No. 4900981 which was issued to Yamazaki et al. on Feb. 13, 1990 (corresponding to the Japanese Laid-open Patent Publication No. 62-147635, published July 1, 1987)
FIGS. 1A and 1B show the support which U.S. Pat. No. 4145633 discloses. In this patent, a plurality of spaced, parallel, substantially semi-cylindrical beads 132 of a rigid material are disposed on one surface of face plate 131 and are surrounded by the phosphor plate. Each of beads 132 fits in the groove 134 defined in a metal strut 133 to avoid a lateral movement of the electrode. One end of each metal strut 133 opposite to the groove 134 is directly compressed into the support 136 of insulative material, such as glass, through a respective hole defined in the shadow mask 135. The phosphor plate, the metal strut 133 and the shadow mask 135 are applied the same voltage. However, since this panel has a construction wherein a contact to the control electrodes having a lower voltage than that of shadow mask 135 is made through the insulating support 136, the application a required high voltage to this panel is not permitted due to the tendency of a spark discharge to occur through the support 136.
Furthermore, because this support 136 is connected to the phosphor plate through the metal strut 133, unless an electrode having a substantially same voltage between shadow mask and phosphor plate exists, the electron beam may be deflected out of its intended trajectory under the influence of the voltage of the support.
FIG. 2 shows the support which U.S. Pat. Nos. 4341980 and 4356427 disclose. Between the metal back layer 143, disposed on fluorescent layer 144, and the third electrode 141, from among a plurality of flat electrodes, a cylindrical insulator 142 as a support is arranged. U.S. Pat. Nos. 4341980 and 4356427 specifically disclose the property required for support 142. If this support 142 is made of a well-known glass material, the support 142 will lose an insulating property because the dielectric property is lowered with time. Therefore, this patent suggests the use of non-alkaline glass as the material for the support. However, the use of glass of such a special composition is disadvantageously costly. In addition, the necessity of the support being processed to assume a rod-like configuration with the use of glass of the special composition renders and in cost. Furthermore, it is inevitable for the rod-like support to be thinner as the pitch between each neighboring pixels on fluorescent layers is reduced. This in turn narrows the electrode-to-electrode distance, resulting in the a reduction in breakdown voltage characteristic.
FIGS. 3A and 3B show the struts disclosed in U.S. Pat. No. 4622492. The envelope of the flat panel display device is divided into a number of modules by means of reinforcement partitions 151. These partitions 151 made of electric insulator have a portion of deflection electrodes 152 and contact the display screen 153. This invention is featured in the envelope having a V-shaped concave groove on its outer surface to make the partitions 151 substantially invisible. However, the display panel of this patent cannot be applied a required high potential for the same reason as that discussed in connection with U.S. Pat. No. 4145633.
U.S. Pat. No. 4622492 also discloses an embodiment of a gas discharge panel. However, this gas discharge panel has a problem in that a discharging ability cannot be maintained stably due to its construction having the reinforcement partitions made of an electric insulator.
FIG. 4 shows the support disclosed in U.S. Pat. No. 4900981. This support 161 comprises a supporting plate 162 and a supporting rod 163 which faces a fluorescent layer 165 on a face plate 164. Because supporting rod 163 made of metal is applied the same potential as a high voltage applied to a fluorescent layer 165, there will be no spark discharge available. However, a spark discharge takes place so often around deflecting electrodes formed on supporting plate 162 made of electric insulator. Particulary, as between electrodes to which is applied a substantially same voltage as that applied to fluorescent layer 165 and adjacent electrodes, spark discharge occurs readily.
Large-sized flat panel display devices of the prior art employ supports arranged inside the panel to hold and prevent the panel from undergoing an implosion by the effect of atmospheric pressure.
However, these supports made of an insulator make it difficult to maintain a sufficient voltage breakdown characteristic since those supports are positioned between an electrode such as a fluorescent layer, applied with a high voltage, and an electrode such as a electrode facing the fluorescent layer to which a voltage lower than that high voltage is applied. It is too difficult to realize a insulator providing a sufficient distance between each electrodes and no visual damage by its own shadow to the display screen.